Method of producing vanillin



Patented Nov. 27, 1951 METHOD OF PRODUCING VANlLLIN John Henry Fisher,St. Catharines, Ontario, and Harry Borden Marshall, Toronto, Ontario,Canada, assignors to The Ontario Paper Company Limited, Thorold,Ontario, Canada No Drawing. Application January 7, 1949, Serial No.69,816. In Canada August 11, 1948 4 Claims. 1

This invention relates to the production of vanillin, acetovanillone andother oxidation products from lignosulfonic acid compounds such as wastesulphite liquor and especially from the same after treatment such thatthe fermentable sugar content thereof has been reduced.

It is well known that lignosulfonic acid compounds can be used toproduce vanillin and other products when subjected to oxidation undersuitable conditions in the presence of caustic soda, or caustic potash.Cross reference is made to the co-pending applications of Marshall andSankey, Serial Number 606,690 filed July 23, 1945 now Patent No.2,516,827 and Serial Number 767,626 filed August 8, 1947 now Patent No.2,544, 999, and to that of Fisher and Marshall filed of even date hereofS. N. 69,815, in which are dis closed methods of effecting production ofvanillin and co-products from lignin-containing substances in aparticularly advantageous manner.

In our co-pending application S. N. 69,815 filed of even date hereof wehave disclosed a method of producing vanillin in which lime is used asthe active alkali. We have now found that the yield of vanillin and ingeneral also the yield of acetovanillone and other related co-productsis substantially increased as the initial concentra-' tion of lignin inthe reaction vesselis decreased. This influence of the dilution of thelignin content of the materials supplied to the reactor could not havebeen predicted according to the known practice in this art and isspecific to the use of lime as the active alkali. The increased yieldwhich can be obtained is sufficient to justify the substantial dilutioneven of such lignosulfonic acid compounds as waste sulphite liquor andalcohol plant effluent. By alcohol plant efliuent we mean the liquorremaining after sulphite liquor has been subjected to fermentation toproduce ethyl alcohol. Since large volumes of waste sulphite liquorand/or alcohol plant efiiuent are produced in normal commercialoperations, the normal tendency in handling these materials on anindustrial scale would be to concentrate them, or otherwise effect anincrease in the lignin content per unit volume as a preliminary step tosuch utilization. The contrary procedure of dilution which we havediscovered as a means of effectively increasing vanillin yield inaccordance with our invention is, therefore, a step which is contrary togenerally accepted practice.

The dilution to which we refer may be cheated by any one or acombination of means, for example, the waste sulphite liquor as drawnfrom the blow pits after discharge from sulphite digester may be dilutedby inclusion of appropriate additions of water used to wash the pulp inthe blow pit; further direct additions of water may be made to thisliquor; the additions of water may be made as part of a subsequentprocessing of the waste sulphite liquor, for example, the fermenta tionof the sugar content thereof to produce ethyl alcohol; the lime used maybe admitted to the reactor in a dilute aqueous slurry; and/or thereactor itself may be subjected to direct steaming. When used for thepurpose of practising our invention any one or a combination of suchmeans or the like are to be considered as lying within the scopethereof.

It will, of course, be apparent that there is a practical limit to thedilution of such a material as waste sulphite liquor beyond which theconcentration of vanillin and co-products (regardless of their yield ona lignin basis) becomes so dilute that their subsequent recovery becomesimpracticable. Examples of experiments which we have performed and whichare herein given will illustrated the range of dilution which we haveemployed and of the yields which we have obtained therefrom.

In this specification the lignin content of lignin-containing substancesis measured in terms of the methoxyl content thereof and in ourexperiments it is assumed that the ratio of methoxyl content to lignincontent of any of the mixtures investigated is 15.5 to 100. Such anassumed ratio is in accordance with current good chemical usage indealing with lignin-containing substances. Whether this assumed ratio isor is not numerically correct is immaterial because the ratio ofmethoxyl to lignin may be reasonably assumed to be constant for anygiven lignin-containing substance. The assumption of the above ratiowill, therefore, serve for purposes of obtaining a valid relative guideto the quantity of lignin in lignin-containing substances.

In practicing our invention we pursue methods disclosed in ourco-pending application S. N; 69,815 filed of even date hereof and usethe apparatus described therein, but in the course of such operations wedilute the reaction mixture in a manner such as hereinbefore stated.

The concentration of lignin in undiluted waste sulphite liquor isdependent in some measure on the sulphite pulping procedure employed,but in general usually is a higher concentration than grams per litrewith concentrations of the order of grams per litre or higher beingtypical.

The following description of experiments which have been performed by uswill serve to illustrate the application and practice of our invention.It is to be understood that our invention is not limited to thematerials and conditions described in these experiments which are to beconsidered as examples only.

In analyzing materials for their vanillin content, two generaltechniques have been employed. The first is a gravimetric procedureinvolving the separation and estimation of vanillin in the form of itsm-nitrobenzoyl hydrazone. This is described by Buckland, Tomlinson andHihbert, Can. J. Research 16B, 54 (1938) and is the more accurate of thetwo procedures but involves a tedious analytical operation. We employether as a solvent in place of trichloro'ethylene as described in theaforementioned reference. The second is a spectrometric method ofanalysis according to the general method of Lemon, Ind. Eng. Chem.,Anal. Ed. 19, 846 (1947). This is a rapid procedure which gives anoverall measure of the substances present which are spectrometricallyactive at approximately 3500 a p., the vanillin being the principalsubstance present which is so active. This much more simple and rapidprocedure has been used in a great deal of our correction factor basedon the ratio of the gravimetric to spectrometric results Where both orthese have been determined for the same type of residue.

A charge of alcohol plant eiliuent and slaked lime diluted with waterwas pumped into the reaction vessel and heated by direct steaming to 170C.-, the lignin concentration of the said charge at the said temperaturebeing 26grams per litre and the volume in the reaction Vessel underreaction conditions 45.6 U. S. gallons. Air was introduced at the rateof 32 lb. per hour for a total reaction time of 100 minutes, of whichminutes was before maximum temperature was reached and 85 minutesthereafter. The pres sure in the reactor vessel was maintained at 153lb. gauge. Samples were withdrawn from the reactor at various timeintervals and analyzed spectrornetrically. The peak vanillin yield wasobtained at 60 minutes reaction time and by the gravimetrie method was6.7% vanillin on a lignin basis.

Previous control experiments with our equipment have established that anobserved temperature of 170 C. corresponds to a steam gauge pressure of103 lb. whenno air is present. By difierence, the partialnon-condensible gas pressure in the reactor was therefore 50 1b. andthecorresponding partial oxygen pressure less than 10 lb.

The above experiment was repeated with the same alcohol plant effluent,varying the lignin concentration by appropriate modifications in thedilution. The results obtained are given in the table below.

Yield of vanillin Grams per Litre 89. 0

Hwo: 9a

- UICOQ sex s: UIQQDN) S In the above table the yields are those asdetermined by the gravimetric method corresponding to the peak yield asindicated by spectrometric analysis.

When in this specification we use the expression lignosulfonic acidcompounds we mean thereby materials derived from lignin when so treatedthat sulfonic acids are formed therefrom, e. g. when lignin-containingsubstances are subjected to the sulphite pulping process, and includingsalts of the said sulfonic acids.

When in the claims we refer to a pH of 12 or greater we have referenceto the pH of a sam- 'ple withdrawn from the reactor after being cooledto room temperature. In the determination of the pH we have used a glasselectrode especially designed to be accurate in the range of highalkalinity measurements.

What we claim as our invention is:

1. A method of producing oxidation products including the calciumderivative of vanillin from lignosulfonic acid compounds, the initiallignin concentration of such compounds in an alkaline aqueous medium,measured as herein prescribed, being not more than 38 grams per litrenor less than 10 grams per litre, the said medium con taining lime asthe active alkali in an amount SlifilCieIlt to maintain the pH of thereaction mixture determined on a sample withdrawn from the reaction zoneand cooled to room temperature in the range not less than 12 to not morethan that of a saturated solution of lime in the same mixture, whichcomprises introducing said compounds into a reaction zone, heating thereaction mixture to a temperature not less than 0., nor more than 200C., maintaining said zone under super-atmospheric pressure, continuouslypassing a gas containing free oxygen in finely dispersed form throughsaid reaction zone, continuously removing residual gas, the rate ofaddition and removal of said gas being such as to maintain a partialpressure of oxygen in said zone of less than 20 lb. per square inch, thetime of said reaction being less than four hours.

2. The process of claim 1 wherein the 1ignosulfonic acid compound issulphite waste liquor.

3 The process of claim 1 wherein the li'gnosulfonic acid compound insulphite waste liquor which has been previously treated to reduce thefermentable sugar content thereof.

4. The process of claim 1 wherein the liquid portion or" the reactordischarge is separated from the solid portion thereof prior toacidification to release free vanillin therefrom.

JOHN HENRY FISHER. HARRY BORDEN MARSHALL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,099,014 Hatch Nov. 16, 19372,187,366 Schulz Jan. 16, 1940 2,434,626 Salvesen et a1. Jan; 13, 1948OTHER REFERENCES 7

1. A METHOD OF PRODUCING OXIDIZATION PRODUCTS INCLUDING THE CALCIUMDERIVATIVE OF VANILLIN FROM LIGNOSULFONIC ACID COMPOUNDS, THE INITIALLIGNIN CONCENTRATION OF SUCH COMPOUNDS IN AN ALKALINE AQUEOUS MEDIUM,MEASURED AS HEREIN PRESCRIBED, BEING NOT MORE THAN 38 GRAMS PER LITRENOR LESS THAN 10 GRAMS PER LITRE, THE SAID MEDIUM CONTAINING LIME AS THEACTIVE, ALKALI IN AN AMOUNT SUFFICIENT TO MAINTAIN THE PH OF THEREACTION MIXTURE DETERMINED ON A SAMPLE WITHDRAWN FROM THE REACTION ZONEAND COOLED TO ROOM TEMPERATURE IN THE RANGE NOT LESS THAN 12 TO NOT MORETHAN THAT OF A SATURATED SOLUTION OF LIME IN THE SAME MIXTURE, WHICHCOMPRISES INTRODUCING SAID COMPOUNDS INTO A REACTION ZONE, HEATING THEREACTION MIXTURE TO A TEMPERATURE NOT LESS THAN 120* C., NOR MORE THAN200* C., MAINTAINING SAID ZONE UNDER SUPER-ATMOSPHERIC PRESSURE,CONTINUOUSLY PASSING A GAS CONTAINING FREE OXYGEN IN FINELY DISPERSEDFORM THROUGH SAID REACTION ZONE, CONTINOUOUSLY REMOVING RESIDUAL GAS,THE RATE OF ADDITION AND REMOVAL OF SAID GAS BEING SUCH AS TO MAINTAIN APARTIAL PRESSURE OF OXYGEN IN SAID ZONE OF LESS THAN 20 LB. PER SQUAREINCH, THE TIME OF SAID REACTION BEING LESS THAN FOUR HOURS.